This proposal describes an experimental approach to study the role of the hormone relaxin in gestation and parturition. Specific projects involve: 1) electrophoretic isolation of specific molecular species of relaxin from crude porcine relaxin preparations; 2) investigations of the biological capabilities of the isolated fractions; 3) use of radioimmunoassay to study levels of the hormone in sera and tissues from normal and experimentally altered animals; 4) utilization of the fluorescein labeled antibody technique to identify cells and tissues that contain relaxin. Four types of animals will be used for comparative purposes in these projects; mice, rats, rabbits, and guinea pigs.